Security light on Chevrolet Impala?

I have a 2002 Impala LS with 134,000 miles on it. This car has always given good service and has never been a problem. But the other weekend I was cleaning out the garage and parked the car outside. It was about 90 degrees out and when I started the car to put it back in the garage, the security light stayed on. The next morning I started the car and the light was off as I drove to work the security light came back on. I drove to work this morning and it stayed off. When I left work the car would not start, it acted like it had a dead battery, but the battery is fine. After a rainstorm came through our area and cooled the area off the car started right up, but the security Light stayed on again. I called a Chevrolet dealer and he said that it may be a fuel pressure regulator problem and asked if it did this when it was hot outside. I said yes that seems to be when this is happening.

Anyone have any ideas on this?